PRAM-3 will evaluate the virologic, immunologic and therapeutic potential of novel combinations of antiretrovirals and better define the pharmacokinetics and drug-drug interactions of therapies included in these regimens. In doing so, the number of therapeutic options available for antiretroviral experienced, HIV infected, clinically stable children will be dramatically increased. The design of this study is a master PRAM linking arm, Phase II, randomized, comparative, open label, multicenter, multi-arm protocol with experimental therapies added in a rolling protocol format. The Primary Objectives are as follows: - To evaluate combination treatment regimens consisting of ddI/NFV/RTV and d4T/NVP/NFV with respect to the change in plasma HIV-1 RNA copy number from baseline to week 48 in stable HIV-infected children with > 16 weeks of prior continuous antiretroviral therapy - To evaluate the safety and tolerance of ddI/NFV/RTV and d4T/NVP/NFV based on laboratory and clinical toxicities - To evaluate individual pharmacokinetics and drug interactions in the first 8 children in ddI/NFV/RTV